In flat roofs of residential, commercial and industrial establishments it is not uncommon to provide a finial, cresting or ridge along the edge which must be sealed against the incursion of water by a flashing. The flashing, which generally engages over the finial, cresting or ridge, is frequently composed of sheet metal such as galvanized iron, copper or aluminum. The sheet metal usually extends beneath the roof covering which is applied along the flat portions of the roof bordering the ridge and may consist of a thick layer of tar, multiple layers of roofing paper or felt, one or more layers of asphalt covered with gravel (gravel roofs), the sealing being effected with roofing cement, molten tar or other bituminous products.
The sheet-metal rim of the roof has expansion characteristics which differ from those of the rest of the building and thus expansion joints are required in the sheet metal rim.
An earlier expansion joint system which can be used for such purposes is described in U.S. Pat. No. 3,123,188 as an expansion joint for metal panels and comprises a pair of profiled edges spanned by an elastomeric strip which seals the gap between the panels. With expansion joints of this type, it has been found that leakage occurs with the passage of time. Investigations have shown that the leakage is a result, in part, of the deterioration of the elastomeric band by exposure to the weather or, more generally, to ambient environment effects. The elastomeric material, generally composed of rubber or a rubber-like synthetic resin material, has an ultraviolet-light sensitivity which causes deterioration with time and frequently also has minimum resistance to chemical contaminants present in air.
The elastomeric material is further characterized by a low resistance to heat and is embrittled when hot tar or hot bitumen is used as the sealing material on the sheet-metal panels. Sprayers capable of depositing liquid sealing materials upon the panels also tend to damage the elastomeric band. There are of course known various heat-resistant materials which, however, have considerable sensitivity to ultraviolet light.